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    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
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    <script>
      /* 
      思路：遍历二叉树每个节点，然后交换其左右子节点即可
      */
      var invertTree = function (root) {
        function preOrder(root) {
          if (!root) return null
          let temp = root.left
          root.left = root.right
          root.right = temp
          preOrder(root.left)
          preOrder(root.right)
        }
        preOrder(root)
        return root
      }
    </script>
  </body>
</html>
